Analysis and modeling of the locomotor central pattern generator as a network of coupled oscillators.

The primary functions of spinal locomotor central pattern generators (CPGs) are to provide oscillatory motor commands to individual joints or segments and to control the precise timing of those commands across all joints or segments for efficient, coordinated locomotor behavior. Our ability to understand the neuronal mechanisms underlying intersegmental coordination has been hampered by the complexity of propriospinal interconnectivity and the paucity of quantitative data on the magnitude and timing of those connections. Theoretical approaches have therefore been employed to discover general rules by which CPG-like oscillator systems must be constructed to produce appropriate coordinated locomotor behavior; the locomotor CPG is represented as a network of oscillators, where each oscillator generates local motor output and interoscillator coupling provides intersegmental coordination. Mathematical analysis of such coupled oscillator systems has provided a number of experimentally testable predictions regarding the link between coupling and coordination. Application of these network-level predictions to the results of electrophysiological experiments has required data analysis methods that can relate the behavior of the in vitro spinal cord to the variables employed by the mathematical model. Hence, our most recent work has focused on developing analytic tools for quantifying the changes in locomotor output that result form experimental manipulations of the propriospinal system in terms of frequency, intersegmental phase, and intersegmental correlation. Results of recent experiments can now be used to put further constraints on the allowable kinds of intersegmental coupling provided by mathematical modeling of the system.